Branches of Microbiology

Branches of Microbiology

i) Bacteriologyii) Virologyiii) Immunologyiv) Paracytologyv) Mycology

Study of bacteria is known as Microbiology

Structure of Bacteria

Essential Structure :

From inside to outside —

i) Nucleus

ii) Cytoplasm

iii) Cytoplasmic membrane

iv) Cell wall

Non essential Structures / Accessory structures are :

i) Fimbria / Pilus. ( Pili-Plural)

ii) Flagella

iii) Spore

iv) Capsule

Draw & Label a typical bacteria

Cell Wall

Peptidoglycan : The strength of cell wall

Is chiefly provided by peptidogycan.

composed of repeating units of N-acityl muramic acid and N-acityl glucosamine with tetrapeptide side chain

Gram Positive Wall

Peptidoglycan of gram positive bacteria is much thicker (multi layered).Teichoic acid and Teichoronic acids water are soluble polymers.

• Other complex polysaccharide.

Gram Negative Wall

• Peptidoglycan (1-2 layers)

• Lipoprotein : It connect the other membrane to peptidoglycan

Outer Membrane Protein (OMP)

• It is a phospholipid bi-layer & contains specific protein.

• Lipopolysaccharide (LPS) consist of a complex lipid called lipid A and polysaccharide.

.

Lipid-A : Toxic portion

Polysaccharide portion : Surface antigent

LPS – is the endotoxin of the gram negative bacteria. The toxicity is associated with lipid and polysaccharide portion represents surface antigen.

Function

1. It prevents osmotic lysis of bacterial cell.

2. It gives shape of the cell.

3. It is associated with its own bio-synthesis.

4. It is antigenic in nature.

5. It helps in cell division.

Spheroplasts : Derived from gram negative bacteria and retains the

remnants of the other membrane.Protoplasts :Derived from gram positive bacteria that completely

lack cell wall.Both one produced by under the influence of cell wall

inhibitors and one osmotically fragile Hypertonic condition is necessary for their maintenance.

L-form :Cell wall deficient forms of bacteria develops either

spontaneously or under the influence of cell wall inhibitors.

May revert back to its normal form.

Cytoplasmic Membrane

It is thin, elastic, semi-permeable layer lies beneath the cell wall. Electron microscope shows three layers forming a “Unit membrane”. The central layer is made of protein molecule and on its either side there are lipid molecules.

Function :

• Selective permeability and transport of solutes.

• Electron transport and oxidative phosphorylation.

• Excretion of hydrolytic enzyme.

• Possess the enzymes and carrier molecules.

• Synthesis of structural components.

Mesosome

Convoluted, multi-laminated, membranous sac like structure formed by invaginations of cytoplasmic membrane. These serve as source of respiratory enzyme.

Types of Mesosomes :

Septal mesosome

Latera; mesosome

The septal mesosome is attached to bacterial chromosome and is involved in DNA segregation and the formation of cross-wall during cell division.

Capsule :

It is an outer well - defined covering of thick condensed, jelly like materials that surrounds the bacterial cell wall.

It is composed of polysaccharide or polypeptide.

Function :i) It prevent phagocytesii) It enhances bacterial virulence, certain bacteria are

pathogenic only in capsulated state.iii) It is antigenic in natureiv) Specific identification of bacteria can be made by

using antiserum against the capsular polysaccharide

All caps are polysaccharide except – bacillus.They are polypeptideCapsulated bacteria: PneumococusKlebsiella pneumoniaBacillus anthrcis (polypeptide)

Glycocalyx

Extracellular polymer forming loose meshwork of fibrils. When these polymers appear to be totally detached from the cell in which other cells may be entrapped, it is called – slime layer.

Flagella

These are filamentous appendages composed of protein protruding through the cell wall.

These are organs of locomotion. Gives antigenesity of bacterial cell

Types :

i) Monotrichous – Single polar flagellum, eg.- vibrio cholerae.

ii) Amphitrichous – Single flagellum attached to each end eg. pseudomonas

iii) Lophotrichous – Tufts of flagella at one end – eg. Spirillum minus.

iv) Peritrichous – Numerous flagella all over the bacterial body. eg. salmonella typhi

Each flagellum consists of three distinct parts:

Basal body

Hook

Filament

The filament lies external to the cell and the hook. Basal body is embedded in the cell envelope. The basal body is attached to the cytoplasmic membrane by ring like structure.

Flagella are antigenic in nature. So, useful in immunological diagnosis of infections.

Fimbria

These are thin, short, straight appendages, extruding from the cytoplasmic mambrane. These are found in some gram negative bacteria and are always arranged peritrichously.

More numerous than flagella.These are antigenic and associated with

virulence.Types :Common (Ordinary) piliSex pili

Function :

i) Adhesion: Pili are organs of adhesion.

ii) Sex pili : These are specialized, longer and responsible for transfer of genetic factor in bacterial conjugation.

Adhesion is the pre requisite for infection.

ResistantSex pilus

Sensitive Resistant

R-factor

X Y Y

Bacterial Spores

Spores are highly resistant, dormant stage of bacteria formed in adverse environmental conditions such as starvation and desiccation.

Spores :

Endospore

Exospore

Structures of Spore:

• Core

• Spore cell

• Cortex

• Coat

• Exosporium

Bacterial spore are always endospore. Fungus spore are exospore.

Spore Vegetative form

Spore forming bacteria : Aerobic : Bacillus Anaerobic : Clostriidia

Germination

Sporulation

Core: Consist of the chromosome, a high concentration of calcium ions and dipicolinic acid.

Mner membrane : Comprises the cytoplasmic membrane of the cell.

Cortex : Consists of loosely cross linked peptidoglycan

Coat : Protein similar to keratin with highly cross linked, disulfide bonds forms a major barrier to chemicals.

Exosporium: Lipo protein membrane.

Shape & Position of Spore :

It may be oval or spherical spore may be central, subterminal and terminal in position.

Resistance: Bacterial spores are highly resistant to ordinary boiling, heating and disinfectants.

Heat resistance of sporea are due to

• Relative impermeability of spore coat

• Low water content, low metabolic activity.

• High concentration of calcium dipicolinic.

• Low enzyme activity.

Germination :

The process of conversion of a spore into a vegetative form. It consist of three stages –

a) Activation by agents which damage the coat such as heat, low pH, abrasion.

b) Initiation

c) Outgrowth

Spore forming bacteria cause severe infection

Plasmid PlasmidAre extra chromosomal double stranded circular

DNA molecules that are capable of replicating independently of the bacterial chromosome

Plasmids carry the genes for following function1. Drug resistance by R factors2. Exotoxin including several enterotoxin3. Metabolic activity. 4. Transfer of genetic material by sex pilli.

TransposonsTransposons

Transposons are pieces of DNA that moves Transposons are pieces of DNA that moves from one site to another , within or between from one site to another , within or between the DNAs of bacteria, plasmid, and the DNAs of bacteria, plasmid, and bacteriophage. bacteriophage.

The can code for drug resistance The can code for drug resistance enzymes,toxin etc.enzymes,toxin etc.